Have a BB with a moderately sized roller in it. It’s a 451 and am running a Holley 950 on it. I’ve tried a number of things but am having trouble with it back firing through the carb when I mash the throttle. Idles great revs great on the primaries but once I move to the secondaries no go. Backfired and nearly stalls the engine. I have the dizzy locked out at 37 degrees. Have tried it anywhere between 35-38 with the same result. I have 30 cc accelerator pumps. On the secondaries I’m using the brownish red pump cam with a #37 squirter. This carb ran great on a buddies BBC with similiar cubes and a big solid cam. Any help is appreciated and if you need more info please let me know. Thanks!